Stackable ball grid array

ABSTRACT

A stackable package to create a 3-dimensional memory array using ball grid array technology. Specifically, memory chips are coupled to a pre-formed packages which have alignment features to allow for the stacking of the ball grid arrays. The alignment features are used to align and orient each package with respect to an adjacent package, substrate or printed circuit board. The alignment features also support the weight of the adjacent package during solder ball reflow to maintain stack height and parallelism between packages. Each memory device is serially connected to the adjacent memory device through the vias and solder balls on each package.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to electrical circuitry and,more particularly, to a stackable packaging system using ball grid arraytechnology.

2. Description of the Related Art

Packaging of electrical circuits is a key element in the technologicaldevelopment of any device containing electrical components. Fine-PitchSurface Mount Technology (FPT) and Pin Grid Array (PGA) technology arewell developed areas of packaging technology. An emerging packagingmethod has been developed using Ball Grid Array (BGA) technology.

BGA technology offers several advantages over FPT and PGA. Among themost often cited advantages of BGA are: reduced co-planarity problems,since there are no leads; reduced placement problems; reduced pasteprinting problems; reduced handling damage; smaller size; betterelectrical and thermal performance; better package yield; better boardassembly yield; higher interconnect density; multilayer interconnectoptions; higher I/Os for a given footprint; easier extension tomultichip modules; and faster design-to-production cycle time.

While BGA technology provides many benefits, there is still a growingdemand for more component functionality in a smaller space. Despite thebenefits provided by BGA technology, BGA is still a surface mounttechnology like FPT and PGA and, thus, is limited by the space availableon the mounting surface. Significant research and development has beendevoted to finding ways to get more and more capabilities into smallerareas. Engineers have been challenged with finding ways to increasehardware capabilities, with memory capacity being one area in whichboard geography is at a particular premium is memory. However,regardless of whether FPT, PGA or BGA is implemented, surface mounttechnologies are limited by the space available on the ceramic substrateor printed circuit board (PCB). As a result, the amount of memory willdisadvantageously be limited by the dimensions of the mounting surface.

The present invention may address one or more of the problems set forthabove.

SUMMARY OF THE INVENTION

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms the invention might take and that these aspects are notintended to limit the scope of the invention. Indeed, the invention mayencompass a variety of aspects that may not be set forth below.

In accordance with one aspect of the present invention, there isprovided a system that includes a processor and a memory device coupledto the processor. The memory device includes a stacked ball grid arrayand memory chips.

In accordance with another aspect of the present invention, there isprovided a stacked ball grid array. The stacked ball grid array containsa plurality of packages made up of some structural dielectric. Eachpackage is coupled to another package and to one or more memory chips.Each package contains a die side for mounting a chip such as a memorydevice, and a wire side. The wire side of the package contains aplurality of solder balls used to couple one package to another. Byusing solder balls to connect the packages, each memory chip can beserially connected by vias contained within the packages.

In accordance with still another aspect of the present invention, thepackage contains alignment features on the die side and wire side. Thealignment features may be male or female and are used for alignment,orientation, and ball support. A die, such as a memory chip, is mountedwithin the alignment features and electrically coupled to the package.Signals are routed from the memory chip to the outside of the packageand connected to adjacent packages through vias and solder balls.

One advantage of the present invention is that it employs BGA technologyto create a Stacked Ball Grid Array (SBGA). The memory chips are mountedto preformed packages, made for example from a molded resin,incorporating BGA technology. As previously discussed, the packages areconstructed such that they contain alignment features. These featuresare oriented on the packages in such a way that allows the packages tobe stacked. The arrangement or the features allow for alignment andorientation of each package with respect to an adjacent package, whilealso providing package support during the stacking and reflow processnecessary to connect the packages. The alignment features providemaintenance of the stack height and parallelism between packages.

Thus, the present invention allows for increased memory capacity withoutrequiring additional surface area on the ceramic substrate or printedcircuit board to which the memory devices are electrically coupled.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention may become apparentupon reading the following detailed description and upon reference tothe drawings in which:

FIG. 1 illustrates a block diagram of an exemplary processor-baseddevice in accordance with the present invention;

FIG. 2 illustrates an exemplary conventional memory array;

FIG. 3 illustrates a side view of a stacked ball grid array (SBGA) inaccordance with the present invention;

FIG. 4 represents an isometric view of the SBGA of FIG. 3;

FIG. 5 illustrates top view of a single stackable ball grid array;

FIG. 6 illustrates a cross-sectional view taken along line 6—6 of FIG.5;

FIGS. 7A, 7B, and 7C illustrate cross-sectional views along line 6—6 ofalternate configurations of alignment features;

FIGS. 8A, 8B, 8C and 8D illustrate top views of alternate orientationfeature configurations; and

FIG. 9 illustrates two SBGAs electrically coupled together.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Turning now to the drawings, and referring initially to FIG. 1, a blockdiagram depicting an exemplary processor-based device generallydesignated by the reference numeral 10 is illustrated. The device 10 maybe any of a variety of different types, such as a computer, pager,cellular telephone, personal organizer, control circuit, etc. In atypical processor-based device, a processor 12, such as amicroprocessor, controls many of the functions of the device 10.

The device 10 typically includes a power supply 14. For instance, if thedevice IO is portable, the power supply 14 would advantageously includepermanent batteries, replaceable batteries, and/or rechargeablebatteries. The power supply 14 may also include an AC adapter, so thedevice may be plugged into a wall outlet, for instance. In fact, thepower supply 14 may also include a DC adapter, so that the device can beplugged into a vehicle cigarette lighter, for instance.

Various other devices may be coupled to the processor 12 depending uponthe functions that the device 10 performs. For instance, a userinterface 16 may be coupled to the processor 12. The user interface 16may include buttons, switches, a keyboard, a light pen, a mouse, and/ora voice recognition system, for instance. A display 18 may also becoupled to the processor 12. The display 18 may include an LCD display,a CRT, LEDs, and/or an audio display, for example. Furthermore, an RFsubsystem/baseband processor 20 may also be coupled to the processor 12.The RF subsystem/baseband processor 20 may include an antenna that iscoupled to an RF receiver and to an RF transmitter (not shown). Acommunications port 22 may also be coupled to the processor 12. Thecommunications port may be adapted to be coupled to a peripheral device24, such as a modem, a printer, or a computer, for instance, or to anetwork, such as a local area network, remote area network, intranet, orthe Internet, for instance. Memory 26 may also be coupled to theprocessor 12.

FIG. 2 illustrates a conventional multichip memory array 30. In thisarrangement, a memory controller 31 is coupled to a-plurality of memorydevices 33. The memory controller 31 and the memory devices 33 aremounted in a planar fashion on the same substrate 35, such as a printedcircuit board. Disadvantageously, this planar layout allows for only alimited number of memory devices 33 to be used depending on the surfacearea of the substrate 35.

To address this shortcoming, FIGS. 3 and 4 illustrate a stacked ballgrid array (SBGA) 40. The SBGA 40 includes a plurality of stackableballgrid array packages 41 that may be stacked one on top of the other.In one embodiment, each package 41 may be made of a structuraldielectric, such as a molded resin. Each package 41 typically has a dieside 42 and a ball side 44. The die side 42 of the package 41 is thechip-mounting surface of the package 41. In an advantageous embodiment,one or more chips 43, such as a memory chip and/or a microprocessorchip, may be mounted on the die side 42 of the package 41. It should beunderstood that the chip(s) 43 may be fully encapsulated, partiallyencapsulated, or bare, depending upon the specific application intendedfor the package 41. The die side 42 may also contain alignment features46, as described hereinafter. The ball side 44 of the package 41includes solder balls 50. The solder balls 50 are electrically coupledto the chip 43 through vias 51 (illustrated in FIG. 6) and/or traces(not illustrated) in the interposer regions 48 of each package 41. Thesolder balls 50 may be used for adhesion, as well as electricalconductivity. The ball side 44 may also contain alignment features 46,as described hereinafter.

In one embodiment, the package 41 contains alignment features 46 on boththe die side 42 and the ball side 44 of package 41, thereby facilitatingstacking of packages 41 in a stable manner. The alignment features 46ensure that each package 41 is aligned with each adjacent package 41 asthe packages 41 are stacked. These alignment features 46 may alsosupport the weight of the package 41 during reflow of the solder balls50 to maintain stack height and parallelism between packages 41.Further, the alignment features 46 may be used to orient the packages 41as described hereinafter.

Referring again to FIG. 3, the SBGA 40 may be attached to a substrate52, such as a printed circuit board. In fact, the SBGA 40 may be alignedusing alignment features 45 which are located on the substrate 52. TheSBGA 40 is electrically coupled to the substrate 52 through the solderballs 50 located on the ball side 44 of the package 41 disposed on thesubstrate 52.

It should be appreciated that each package 41 may contain electricalrouting, such as the vias 51 illustrated in FIG. 6 for example,connected to at least some of the solder balls 50 so that electricalsignals can pass serially from one package 41 to the next. For example,it may be desirable in certain applications to route signals common toeach package, such as V_(cc) and ground, serially through the stack ofpackages 41. In other applications, it may be desirable to route allsignals serially through the stack of packages 41. In one embodiment,for instance, each memory chip 43 may be enabled singularly. That is,only one memory chip 43 in the SBGA 40 will be used at one time so thatthe selected chip 43 utilizes the signals received by the SBGA 40. Withmemory chips 43 mounted on the packages 41 and connected through thevias 51 and solder balls 50, the SBGA 40 forms a three dimensionalmemory array. As memory requirements for a system increase, more memorydevices 43 can be added by adding more packages 41 to the stack, withoutincreasing the amount of surface area required on the substrate 52.Indeed, it should be appreciated that the height of the stack ofpackages 41 is primarily determined by the thickness of the interposerregions 48 and the diameter of the solder balls 50.

FIG. 5 illustrates the package 41 as seen from the die side 42. As canbe seen, a memory chip 43 can be mounted within the alignment features46. In one embodiment, the interposer regions 48 containing the solderballs 50 may be located on opposing sides of the region containing thememory die 43 and the alignment features 46. In this embodiment, thesolder balls 50 are arranged in four columns by eleven rows on one sideof the die region 60 and in three columns by eleven rows on the otherside of the die region 60. However, it should be appreciated thatalternate solder ball 50 arrangements can be used. For example, thesolder balls 50 may be arranged in any suitable row and columnconfiguration in the interposer regions 48 or around the entireperimeter of the package 41.

FIG. 6 illustrates a cross-sectional view of a single package 41 takenalong line 6—6 in FIG. 5. In this illustration, the die side 42 of thepackage 41 includes male alignment features 46 a, while the wire side 44of the package 41 includes complimentary female alignment features 46 b.However, it should be appreciated that alternate package configurationsmay be used. As illustrated in FIG. 7A, the die side 42 of the package41 a may contain male alignment features 46 c, and the ball side 44 maycontain male alignment features 46 d. Another package configuration 41 bcontains female alignment features 46 e on the die side 42, andcomplimentary male alignment features 46 f on the ball side 44 of thepackage 41 b, as illustrated in FIG. 7B. Still another packageconfiguration 41 c contains female alignment features 46 g on the dieside 42, and female alignment features 46 h on the ball side 44 of thepackage 41 c, as illustrated in FIG. 7C. In regard to the packagesillustrated in FIGS. 6 and 7B, the same type of packages may be stackedto form an SBGA. In regard to the packages illustrated in FIGS. 7A and7C, these types of packages may be stacked in an alternating fashion toform an SBGA.

As previously described, each package 41 typically contains somearrangement of solder balls 50 arranged on the ball side 44. In apreviously described embodiment, the number of columns of solder balls50 is different on each side of the memory die 43 to help prevent usererror in stacking the packages 41 to create the SBGA 40. In thisconfiguration, the orientation features 46 may be arranged symmetricallyabout the chip 43 with little likelihood of stacking the packages 41 inerror. However, in an alternate embodiment, the solder balls 50 may bearranged symmetrically about chip 43. In this instance, the alignmentfeatures 46 can be arranged asymmetrically in order to insure that thepackages 41 are oriented correctly and to prevent stacking errors inbuilding the SBGA 40. Alignment refers to the positioning of one package41 with respect to another package 41 or substrate 52 while orientationrefers to the rotational positioning of a package 41 about an axis whichis perpendicular to the substrate 52. Proper alignment and orientationare typically desirable to insure electrical conductivity from onepackage 41 to the next.

FIGS. 8A, 8B, 8C, and 8D illustrate alternate alignment featureconfigurations which provide an orientation function. As previouslydescribed, the alignment features 46 may be arranged symmetrically aboutthe die region 60. An alternate configuration of region 60 a may arrangethe alignment features 46 asymmetrically about the side 42. Stillanother alignment feature configuration 60 b may use a different numberof alignment features 46 arranged asymmetrically about the perimeter ofthe die region 60 b. Still another alignment feature configuration 60 c,may introduce a different shape to one of the alignment features 46 inorder to prevent any stacking errors. By using asymmetrical featureconfiguration, or using one uniquely shaped alignment feature 66, eachpackage 41 will have only one position in which it can be properlycoupled to another package 41 or mounting surface 52. Thus, the risk ofimproperly placing the package 41 is greatly reduced.

While a single SBGA 40 has been described, it should be appreciated thatmore than one SBGA 40 may be used in a given device 10. As illustratedin FIG. 9, one SBGA 80 may be coupled to one or more SBGAs, such as theSBGA 82, on a substrate 84 through a shunt circuit or through some lowimpedance element, such as a metal trace on the substrate 84. Typically,all such SBGAs 80 and 82 are serially connected. By coupling a pluralityof SBGAs together, a device 10 may further exploit the advantages ofadded performance capabilities within the confines of a discrete surfacearea.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

What is claimed is:
 1. A system comprising: a processor; and a memorydevice operatively coupled to the processor, the memory devicecomprising a plurality of vertically stacked ball grid arrays, each ballgrid array having a memory chip, and wherein the vertically stacked ballgrid arrays comprise: a plurality of packages, each of the plurality ofpackages comprising a plurality of non-metal mateable alignmentfeatures, and wherein each of the plurality of packages is physicallycoupled to another of the plurality of packages; and a plurality ofmemory chips, each of the plurality of memory chips physically coupledto a respective one of the plurality of packages.
 2. The system, as setforth in claim 1, wherein each package comprises: a molded resin bodyhaving a die side and a ball side.
 3. The system, as set forth in claim2, wherein each package comprises: a plurality of first mateablealignment features on the die side of the package; and a plurality ofsecond mateable alignment features on the ball side of the package. 4.The system, as set forth in claim 3, wherein the plurality of firstmateable alignment features are male and the plurality of secondmateable alignment features are female.
 5. The system, as set forth inclaim 3, wherein the plurality of first mateable alignment features aremale and the plurality of second mateable alignment features are male.6. The system, as set forth in claim 3, wherein the plurality of firstmateable alignment features are female and the plurality of secondmateable alignment features are male.
 7. The system, as set forth inclaim 3, wherein the plurality of first mateable alignment features arefemale and the plurality of second mateable alignment features arefemale.
 8. The package, as set forth in claim 3, wherein the pluralityof first mateable alignment features and the plurality of secondmateable alignment features orient adjacent packages in a uniquelocation.
 9. The package, as set forth in claim 8, wherein the pluralityof first mateable alignment features and the plurality of secondmateable alignment features are arranged asymmetrically.
 10. Thepackage, as set forth in claim 8, wherein the plurality of firstmateable alignment features and the plurality of second mateablealignment features comprising of at least one unique alignment feature.11. The package, as set forth in claim 3, wherein the plurality of firstmateable alignment features and the plurality of second mateablealignment features support adjacent packages during solder ball reflow.12. The system, as set forth in claim 1, wherein each of the pluralityof packages is electrically coupled to another of the plurality ofpackages using solder balls.
 13. The system, as set forth in claim 12,wherein each of the plurality of packages comprise vias extendingtherethrough to connect solder balls of adjacent packages serially. 14.A memory board comprising: a substrate; and a memory device operativelycoupled to the substrate, the memory device comprising a plurality ofvertically stacked ball grid arrays, each ball grid array having amemory chip, and wherein the vertically stacked ball grid arrayscomprise: a plurality of packages, each of the plurality of packagescomprising a plurality of non-metal mateable alignment features, andwherein each of the plurality of packages is physically coupled toanother of the plurality of packages; and a plurality of memory chips,each of the plurality of memory chips coupled to a respective one of theplurality of packages.
 15. The memory board as set forth in claim 14,wherein the substrate is a printed circuit board.
 16. The memory board,as set forth in claim 14, further comprising a memory controlleroperatively coupled to the memory device and to the substrate.
 17. Thememory board, as set forth in claim 14, wherein the package comprises: amolded resin body having a die side and a ball side.
 18. The memoryboard, as set forth in claim 17, wherein the molded resin packagecomprises: a plurality of first mateable alignment features on the dieside of the package; and a plurality of second mateable alignmentfeatures on the ball side of the package.
 19. The memory board, as setforth in claim 18, wherein the plurality of first mateable alignmentfeatures are male and the plurality of second mateable alignmentfeatures are female.
 20. The memory board, as set forth in claim 18,wherein the plurality of first mateable alignment features are male andthe plurality of second mateable alignment features are male.
 21. Thememory board, as set forth in claim 18, wherein the plurality of firstmateable alignment features are female and the plurality of secondmateable alignment features are male.
 22. The memory board, as set forthin claim 18, wherein the plurality of first mateable alignment featuresare female and the plurality of second mateable alignment features arefemale.
 23. The package, as set forth in claim 18, wherein the pluralityof first mateable alignment features and the plurality of secondmateable alignment features orient adjacent packages in a uniquelocation.
 24. The package, as set forth in claim 23, wherein theplurality of first mateable alignment features and the plurality ofsecond mateable alignment features are arranged asymmetrically.
 25. Thepackage, as set forth in claim 23, wherein the plurality of firstmateable alignment features and the plurality of second mateablealignment features comprising of at least one unique alignment feature.26. The package, as set forth in claim 18, wherein the plurality offirst mateable alignment features and the plurality of second mateablealignment features support adjacent packages during solder ball reflow.27. The memory board, as set forth in claim 14, wherein each of theplurality of packages is electrically coupled to another of theplurality of packages using solder balls.
 28. The memory board, as setforth in claim 27, wherein each of the plurality of packages comprisevias extending therethrough to connect solder balls of adjacent packagesserially.
 29. The memory board, as set forth in claim 14, wherein afirst ball grid array is coupled to the second ball grid array.
 30. Thememory board, as set forth in claim 14, wherein the first ball gridarray is serially coupled to the second ball grid array.